As means for supplying fuel in an atomized state to combustion chambers in an internal combustion engine such as a diesel engine, fuel injection nozzles are generally used. Such fuel injection nozzles, as disclosed for example in Japanese Unexamined Patent Publication No. S.59-200063, have had a construction wherein a conical pressure-receiving surface is formed at the tip end of a needle valve axially slidably received inside a nozzle body and the needle valve is opened by a fuel pressure being made to act on this pressure-receiving surface and fuel is injected into a combustion chamber of the engine through a plurality of nozzle holes formed in the tip of the nozzle body.
However, with this construction, the fuel injection pressure, the injected amount and the injection speed are generally determined by a fuel injection pump, and furthermore it is not possible to increase or decrease the total nozzle hole area. Consequently, during low-speed running of the engine the fuel injection pressure decreases and during low-load running of the engine the injection time becomes short and it is not possible to maintain a good combustion state, and it has been difficult to promote fuel combustion and achieve improvements in output and fuel consumption and reductions in combustion noise and NOx emissions.
As a measure to overcome this, in Japanese Unexamined Patent Publication No. H.4-76266, a variable nozzle hole fuel injection nozzle is proposed. In this related art, a well is formed in the tip part of a nozzle body and a plurality of nozzle holes (eight) connecting with the well are formed spaced in the circumferential direction in a wall enclosing the well. A rotating shaft passes through a through hole formed axially down the center of the needle valve, a tip portion of this rotating shaft is positioned in the well, and a plurality of channels (four) which connect a fuel pressure chamber inside the well to the nozzle holes when the needle valve opens are provided in the rotating shaft. By rotation of this rotating shaft, the number of open nozzle holes is switched between eight and four.
However, with this related art, because the rotating shaft itself is used as a rotary valve, there have been problems in that when there is a machining error the whole shaft becomes a defective product and that it is liable to stop rotating smoothly due to bending or twisting. Furthermore, the wall forming the well forms a straight cylinder parallel with the nozzle axis, and the rotating shaft serving as the rotary valve is also cylindrical. Consequently, it has been difficult to fix the position of the rotating shaft constituting the rotary valve during fuel injection. That is, even when the nozzle holes have been adjusted to a required degree of opening by the angle of the rotating shaft being changed the rotating shaft easily slips undesirably in its direction of rotation about its axis when a high fuel injection pressure acts at the nozzle holes. Consequently, it has not been possible to avoid the positional relationship between the nozzle holes and the channels slipping and the nozzle hole area becoming larger or smaller than the set size.
For this reason, in the related art there has been the problem that it has been difficult to accurately carry out control of the total nozzle hole area in accordance with the load and speed of the engine. In particular, to effect optimal fuel combustion of the engine it is preferable to control the injection rate, conducting a pilot injection before a main injection, but with the related art described above it has been practically impossible to realize an injection pattern of pilot injection--no injection--main injection.
Also, because as described above there is no mechanism for fixing the rotary shaft serving as a rotary valve during fuel injection, in the related art there has been the problem that a large and relatively high-torque motor is needed to drive the rotating shaft and consequently the fuel injection nozzle becomes large.
With regard to pilot injections, a control mechanism in a jerk-type fuel injection device is proposed in Japanese Unexamined Patent Publication No. H.7-77124. However, in this related art, because the fuel injection amount and the injection period and so on of the pilot injection are determined by the relative positions of a plunger and a leak hole of a fuel injection pump, there has been the problem that the degree of freedom of the various parameters is small. In Japanese Unexamined Patent Publication No. H.7-54730 a solenoid-driven fuel injection nozzle is proposed, but in this related art there has been the problem that it is not possible to apply an optimal nozzle hole area to a pilot injection.